1. Technical Field to Which the Invention Belongs
The present invention relates to a vehicle control system for controlling a vehicle on the basis of a road shape, as decided on the basis of map data comprised of a set of coordinate points obtained by a navigation system.
2. Discussion of Relevant Art
In Japanese Patent Laid-Open No. 6-36187, there is well known a technique in which a control system decides whether or not a subject vehicle can pass a curve ahead thereof in its running direction at the current speed by estimating the radius of curvature of the curve on the basis of map data obtained by a navigation system, so that a warning or automatic deceleration is performed if the system decides that the curve is not passable.
Here, the aforementioned well known technique decides whether or not the vehicle can pass a curve, by employing the radius of curvature of the curve as a parameter. Even if curves have the same curvature radius R, as shown in FIGS. 7A to 7C, the passage is easy for a curve having a smaller length R.multidot..SIGMA..theta. (as should be referred to FIG. 7A), but the passage is difficult for a curve having a larger length R.multidot..SIGMA..theta. (as should be referred to FIG. 7C). In order to properly decide whether or not a curve can be safely passed, therefore, it is necessary to consider not only the curvature radius of the curve but also the length of the curve.
According to the known technique, when a curve is difficult to pass, the vehicle speed is automatically reduced to pass the curve. In this case, any voluntary decelerating operation or steering operation of the driver and the aforementioned automatic deceleration may interfere with each other to give the driver an unfamiliar or unpleasant feeling.